1. Field of the Invention
This invention relates to an inverter apparatus which is combined with a battery employed in a non-failure power unit and the like.
2. Description of the Prior Art
FIG. 1 is a circuit diagram of an inverter apparatus combined with a conventional battery which has been shown in, for example, the thyristor usage manual P-406 (published by OHM Co. Ltd. on Sept. 30, 1988). In FIG. 1, reference numeral 1 is an input terminal connected to an AC power source not shown, 2 a rectifier which is constituted by thyristors 2a to 2d controlled by a control unit not shown to convert an AC voltage supplied to the input terminal into a DC voltage, 3 a reactor which absorbs ripple components of the DC voltage, 4 a capacitor which absorbs ripple components of the DC voltage, 5 an inverter which is constituted by self-arc-extinguishing type semiconductors 5a to 5d such as transistors etc. to convert a DC voltage obtained across the capacitor 4 into an AC voltage, 6 a control circuit which controls the inverter 5 and varies an output AC voltage, 7 and 8 are a reactor and a capacitor, respectively, both of which constitute a filter for absorbing ripple components of the output AC voltage of the inverter 5, 9 is an AC output terminal, and 10 a battery which is connected in parallel to the capacitor for absorbing ripple components of the DC voltage.
Next, the operation will be described. When an AC power source connected to the input terminal 1 is normal, an input AC voltage is converted into a DC voltage by the rectifier 2, and the converted DC voltage is controlled to a desirable value by the phase control of the thyristors 2a to 2d.
The DC voltage contains ripple components caused by rectifying the AC voltage. But, the ripple components are absorbed in the reactor 3 and the capacitor 4 to supply a DC voltage having a little amount of ripple components to the inverter 5.
The inverter 5 converts the DC voltage into a predetermined AC voltage, which is controlled by the control circuit 6 so as to become a desirable voltage and a desirable waveform by switching control of transistors 5a to 5b.
The output AC voltage of the inverter 5 contains ripple components due to switching of the transistors 5a to 5d. But, the ripple components are absorbed by the reactor 7 and the capacitor 8, and an AC voltage having no ripple component substantially is output to the output terminal 9.
The capacitor 4 in the DC circuit also absorbs a ripple current generated on the DC side by the inverter 5. Also, the battery 10 connected to the DC circuit is being floating-charged in this state. Since, if a charging current of the battery 10 contains ripple components, heat due to the ripple components is generated in the battery 10, the ripple components are suppressed so as to be reduced below a predetermined value by the reactor 3.
On the other hand, in the case where the AC power source is subjected to power failure, since a DC voltage is supplied to the DC circuit from the battery 10, the inverter 5 converts the DC voltage into an AC voltage and output the AC voltage. The output terminal 9 is continuously supplied with an AC voltage which is fed to load devices irrespective of power failure in the input AC power source. That is, the inverter apparatus operates as a non-failure power unit. Since a conventional inverter apparatus is constituted as described above, a reactor having a large inductance has needed to be employed for the reactor 3. In other words, even if the DC circuit contains a little amount of ripple components, the inverter 5 is capable of outputting an AC voltage which is not influenced by the ripple components. But, in order to reduce ripple components in a charging current of the battery 10, the large-sized reactor 3 having a large inductance needs to be employed.